Mr Barnier met MPs earlier this week and his remarks were published on Friday.

He said that if a backstop ever had to be implemented goods being moved from and to Northern Ireland from elsewhere in the UK would have to be subject to "controls".

He insisted that such controls would not amount to a border and pointed out that there are already checks on some products, such as livestock, coming into Northern Ireland from Great Britain.

Image copyrightAFPImage caption
There is uncertainty about how the Irish border will operate when the UK leaves the EU

Mr Barnier said any new checks could take place at ports in Great Britain or on ships and could be "simplified in technological terms".

He added he had asked the UK for details of trade flows into Northern Ireland so it would be clear what volume of goods could be involved and how much trade between Great Britain and NI comes via Dublin Port.

Mr Barnier said: "What we want is a precise list of the nature, the location of existing controls in Northern Ireland and what volumes are involved."

He acknowledged that it would need a joint approach with the UK government if the issue is to be de-dramatised.

"This will require an effort on both sides, that we should be able to de-dramatise this backstop by describing what it will mean on the ground."

In recent weeks Mr Barnier has suggested the backstop could be "improved" but has given no indication that the EU is open to changing its substance.